Developmental disorders of the human cerebral cortex underlie 15-40% of cases of epilepsy, especially intractable pediatric epilepsy. Hence, a powerful genetic approach to the understanding of these epilepsies, as well as to the study of cerebral cortical development, relies upon the identification of the causative genes in disorders of neuronal migration. Recent work from our lab and simultaneous work from other labs has identified mdab1, a murine homologue of Drosophila disabled (dab), as the gene mutated in the scrambler mouse. Moreover, we have recently discovered a novel gene, doublecortin (DBC N), that is mutated in patients with the double cortex/X-linked lissencephaly syndrome, DC/XLIS (Gleeson et al., 1998). Since both of these predicted proteins appear to lack intrinsic enzymatic activity, their cellular mechanism of action is not obvious, and they likely act via protein-protein interactions with other, as yet unidentified, proteins. The overall goal of this proposal is to analyze the cellular role of mDab1 and Dbcn in neuronal migration, and their relationship to the previously identified LIS1 gene which is mutated in human lissencephaly of the Miller-Dieker type. Specific aim 1 will screen DC/XLIS patients for mutations in DBCN and correlate the positions of mutations with the predicted structure of Dbcn protein and the severity of clinical phenotypes. This should help identify amino acid residues critical for Dbcn function and potential functional motifs of the protein. Specific Aim 2 will determine the pattern the pattern of expression of DBCN mRNA and protein, in order to test hypotheses about where and when the protein is required. Specific Aim 3 will analyze the potential phosphorylation of Dbcn by Abl, and identify protein-protein interactions between Abl, mDab1, Dbcn, and LIS1, because of evidence that Dbcn and mDab1 form part of a signaling pathway that relies on the tyrosine kinase c-Abl. Specific Aim 4 will identify additional proteins that interact directly with Dbcn, Lis1 and mDab1 through yeast two-hybrid screens and co-immunoprecipitation. These screens may identify additional proteins that play critical roles in guiding migrating neurons, and these additional genes will be candidate genes for other human disorders of cerebral cortical development.